Nanoparticle composites have broad industrial application, including use in composite materials, polymer composites, materials science, resins, films, coatings films, reinforced polymer composites, transparent electrodes for displays and solar cells, electromagnetic interference shielding, sensors, medical devices and pharmaceutical drug delivery devices, armor, and aeronautical and mechanical materials and surfaces. For example, in the field of semiconductors and electronic devices, nanoparticles, and specifically, conductive nanoparticles of carbon, metals and the like, have been known and enabled to the industry for many years. Examples of US patent disclosures of such particles and processes are provided, by way of non-limiting examples, in U.S. Pat. Nos. 7,078,276; 7,033,416; 6,878,184; 6,833,019; 6,585,796; 6,572,673; 6,372,077. Also, the advantages of having ordered nanoparticles in these applications are well established. (See, for example, U.S. Pat. No. 7,790,560). By way of another example, the combination of nanoparticles and liquid polymers has been found to improve important properties of rubber articles, such as vehicle tires, and in particular, the tread portion of vehicle tires (see U.S. Pat. No. 7,829,624). Furthermore, the physical properties that can potentially be achieved by polymer composites employing nanoparticles include lighter weight materials with improved strength and electrical and thermal properties. These properties can be of great value in many fields. For example, use in body armor, such as helmets and in aeronautics, is of particular importance.
Nanoparticles can be grouped into structures, including nanotubes. Nanoparticles, and in particular, nanotubes have substantial potential for enhancing the strength, elasticity, toughness, electrical conductivity and thermal conductivity of polymer composites, however incorporation of nanoparticles into composites has been difficult. Nanoparticles can include single-walled nanotubes, double-walled nanotubes, and/or multi-walled nanotubes. The use of single-walled carbon nanotubes in polymer composites has been desirable and yet wrought with complications. For example, nanotubes have a tendency to aggregate, which impairs dispersion of the nanotubes. Non-uniform dispersion can present a variety of problems, including reduced and inconsistent tensile strength, elasticity, toughness, electrical conductivity, and thermal conductivity. Generally, preparation of most polymer composites incorporating single-walled carbon nanotubes has been directed at achieving well-dispersed nanotubes in polymers using methods such as mechanical mixing, melt-blending, solvent blending, in-situ polymerization, and combinations of the same. Attempts to create homogenous aqueous dispersions of single-walled carbon nanotubes have been by using certain water-soluble polymers that interact with the nanotubes to give the nanotubes solubility in aqueous systems. See M. J. O'Connell et al., Chem. Phys. Lett. 342 (2001), p. 265. Such systems are described in International Patent Publication, WO 02/016257, published Feb. 28, 2002, and incorporated herein by reference. However, these attempts have not been fully able to provide a dispersion of nanotubes in polymer composites at the desired level of dispersion. This is due in part to multiple factors. For example, nanoparticles, particularly carbon nanotubes and single-walled carbon nanotube, have a tendency to bundle together, which leads to nonuniform dispersion. Another factor is that nanoparticles, in particular nanotubes, often have relatively fragile structures and many of the existing dispersion methods, such as mixing and intense or extended ultrasonication, damage the structure of the nanoparticles. Furthermore, while not wishing to be bound to this theory, it is believed that the geometrical shape of many nanoparticles and intramolecular forces contribute to less uniform dispersion; however, this could alleviated if the nanoparticles were aligned.
Previous attempts have been made to align the nanoparticles and polymers, in particular carbon nanotubes. One of the attempted methods has been the use of magnetic fields. However, it was found that the application of a magnetic field to align polymers and polymer/nanoparticle composites did not work because nanoparticles, in particular carbon nanotubes, do not align on their own in a magnetic field. Other attempts have included the use of nanotubes functionalized with magnetically sensitive groups, including, for example, Ni-coated nanotubes. However, this attempt failed as the functionalized nanotubes were found to have less strength and a decrease in other mechanical properties. This is at least in part due to the fact that once functionalized, the conjugated structure of the nanotubes is broken, which results in changes in surface properties.
U.S. Pat. No. 7,803,262 discusses methods for aligning carbon nanotubes and for making a material comprising these aligned nanotubes. One method discussed involves adsorbing magnetic nanoparticles with carbon nanotubes dispersed in a fluid medium. However, the methods disclosed have several limitations including the attempt to magnetically align nanotubes by adding magnetic particles into a solution. As a result of the method employed, there is poor dispersion, which results in the materials lacking desired properties.
Similarly Chinese Application No. 200510112180 discusses methods for aligning carbon nanotubes and for making a material comprising these aligned nanotubes. However, the methods disclosed have several limitations including, for example, teaching coating the carbon nanotubes with a magnetic material. This method results in less uniform dispersion and poorer mechanical properties than the methods of the present application.
Likewise, Korean Application No. KR20090094306 discloses a method for preparing a carbon nanoparticles-polymer composite by mixing a carbon nanoparticle dispersion with a polymer solution containing magnetic particles to prepare a composite. However, the methods disclosed have several limitations including, for example, teaching addition of the magnetic particles to the polymer solution. This method results in less uniform dispersion and poorer mechanical properties than the methods of the present application.
More recently, in related research, it was found that nanotubes could be magnetically aligned in nanofluids, such as nanogreases and nanolubricants by employing metal oxides in the fluids. See U.S. Pat. No. 8,652,386. However, none of these attempts have brought about the successful magnetic alignment of nanoparticles in polymer composites.
Accordingly, there is a great need for the development of polymer composites with nanoparticles that are more uniformly dispersed and exhibit improved physical properties, such as increased tensile strength, elasticity, toughness, electrical conductivity, and thermal conductivity. Furthermore, there is a need to develop methods of magnetically aligning nanoparticles, in particular carbon nanotubes, in polymer composites.
Thus, an object of the invention is to provide nanoparticle composites with improved dispersion of nanoparticles, preferably in more uniform dispersion.